A membrane contactor may be used for many purposes, including but not limited to, removing entrained gases from liquids, debubbling liquids, filtering liquids, and adding a gas to a liquid. Membrane contactors are known to be used in many different applications, for example, a membrane contactor may be used in removing entrained gases from inks used in printing.
Membrane contactors may also provide a means of accomplishing gas/gas, gas/liquid, and liquid/liquid (which can encompass liquid/dissolved solid) separations, transfers or additions. Membrane contactors typically are used to bring two immiscible fluid phases—for example, a first liquid and a second liquid, or a gas and a liquid—into contact with one another to effect separation and/or transfer of one or more components from one fluid to the other.
A hollow fiber membrane contactor typically includes a cylindrical bundle or mat of microporous hollow fibers, and a rigid cylindrical shell or housing enclosing the fiber bundle. The shell may be provided with multiple ports, for example, four fluid ports: an inlet for introducing the first fluid, an outlet for discharging the first fluid, an inlet for introducing the second fluid, and an outlet for discharging the second fluid. The hollow fibers may be potted on both ends, within the housing, to form polymeric tube sheets with the fiber bores opening on each end into common first and second end cap portions of the shell. In a “tube-side” or “lumen-side” contactor, the first end cap may contain the inlet for the first fluid, which is designated the “tube-side” or “lumen-side” fluid because it is the fluid that passes through the internal lumens of the fibers. The second end cap contains the outlet for discharging the lumen-side fluid. The second fluid, designated the “shell-side” fluid, typically enters and exits the housing through inlet and outlet ports arranged between the tube sheets, whereby the shell-side fluid contacts the external surfaces of the fibers. The shell-side fluid flows through the interstices between fibers of the fiber bundle, and may be directed to flow parallel or perpendicular to the fiber length.
In a “shell-side” contactor, the contactor may include a central core which passes through the end caps and has a first end serving as the inlet for the first fluid, which is designated the “shell-side” fluid because it is the fluid that passes over the exterior or shell of the hollow fibers. The first end cap may contain the inlet for the second fluid, which is designated the “tube-side” or “lumen-side” fluid because it is the fluid that passes through the internal lumens of the fibers. The second end cap contains the outlet for discharging the lumen-side fluid. The first fluid, designated the “shell-side” fluid, typically enters and exits the housing through inlet and outlet ports (open ends) of the perforated core, and typically exits and re-enters the perforations in the core between the tube sheets whereby the shell-side fluid contacts the external surfaces of the fibers. The shell-side fluid flows through the interstices between fibers of the fiber bundle, and may be directed to flow parallel or perpendicular to the fiber length.
Because the tube sheets separate the lumen-side fluid from the shell-side fluid, the lumen-side fluid does not mix with the shell-side fluid, and the only transfer between the lumen-side fluid and the shell-side fluid occurs through the walls of the hollow fibers. The fine pores in the fiber wall are normally filled with a stationary layer of one of the two fluids, the other fluid being excluded from the pores due to surface tension and/or pressure differential effects. Mass transfer and separation are usually caused by diffusion, which is driven by the difference in concentration of the transferring species between the two phases. Typically, no convective or bulk flow occurs across the membrane.
In the case of gas/liquid separations, membrane contactors are typically fabricated with hydrophobic hollow fiber microporous membranes. Since the membranes are hydrophobic and have very small pores, liquid will not easily pass through the pores. The membranes act as an inert support that brings the liquid and gas phases into direct contact, without dispersion. The mass transfer between the two phases is typically governed by the difference in partial pressure of the gas species being transferred.
For liquid systems, the liquid/liquid interface at each pore is typically immobilized by the appropriate selection of membrane and liquid phase pressures. In this case, the membrane also acts as an inert support to facilitate direct contacting of two immiscible phases without mixing.
Such known mainly cylindrically shaped membrane contactors can be utilized for a variety of applications, including the separation of a component from a fluid or transferring a component of one fluid to another. For example, a membrane contactor can be used in removal of contaminants from an effluent stream. In many industrial processes, a contaminated effluent stream is generated as a by-product. In view of environmental concerns, the desire to separate components, the need to protect equipment, and/or efforts to improve process efficiency, it is often necessary or desirable to, for example, remove one or more components or contaminants from the effluent stream so that the component or contaminant does not pollute the environment, negatively effect equipment, or so that it may be recycled. Existing industrial processes frequently must be upgraded to reduce environmental emissions and/or increase efficiency. Therefore, a need often arises for a process and system that can be economically retrofit to an existing plant to reduce emissions, protect equipment, recycle, or improve efficiency.
At least certain existing membrane contactors have been found less than fully satisfactory in particular applications, for certain conditions, or the like. For example, most shell-type contactors typically must operate at elevated pressures. Accordingly, a need exists for an improved hollow fiber membrane contactor having improved design or characteristics over known membrane contactors, for use in particular applications, for use in certain conditions, and/or the like. It is to the provision of a porous hollow fiber membrane device and/or method meeting these and/or other needs that at least selected embodiments of the present invention may be directed.
The use of porous materials for the selective passage of gases and blockage of liquids is known. For example, LIQUI-CEL® hollow fiber membrane contactors, sold by Membrana-Charlotte a division of Celgard, LLC of Charlotte, N.C., are used for degassing or debubbling liquids. More particularly, LIQUI-CEL® membrane contactors are used extensively for deaeration of liquids in the microelectronics, pharmaceutical, power, food, beverage, industrial, photographic, ink, and analytical markets around the world.
The use of porous materials for the selective passage of humidity (moisture vapor) and blockage of liquid water, liquid desiccant, or other aqueous solutions may be known. In such liquid-desiccant systems, temperature and humidity may be controlled by a salt solution (or desiccant) which absorbs or emits water vapor.
The use of porous materials for the selective passage of water vapor (heat and moisture) and the blockage of gasses (exhaust and intake gases) may be known in connection with energy recovery ventilation (ERV) wherein heat and humidity are exchanged between make-up and exhaust air in a ventilation system.
The use of a membrane with a gas permeable separation layer such as PMP or silicone is known for selective gas/gas and gas/liquid exchange. Such applications can be used to separate selective gasses such as water vapor from an air stream.
While possibly certain such porous materials for the selective passage of gases or humidity (moisture vapor) and blockage of liquid water or salt water may have met with commercial success, such as RO membranes sold by Dow Chemical, or expanded polytetrafluoroethylene (ePTFE) membranes sold by W. L. Gore, BHA, and others, there is a need for improved porous materials so that they may be used in a wider spectrum of applications, may perform better for particular purposes, under certain conditions, or the like. Also, a need exists for an improved membrane contactor having improved design or characteristics over known membrane contactors, for use in particular applications, for use in certain conditions, and/or the like. It is to the provision of a porous membrane device and/or method meeting these and/or other needs that at least certain selected embodiments of the present invention may be directed.